The present invention relates to a rubber article, especially a tire, an air spring, or a drive belt, comprising at least one basic, amino-group containing, aromatic anti-oxidant and having a non-black areal member applied to the surface of the rubber article. The areal member is, for example, in the form of symbols such as letters and/or numbers and/or trademarks and/or pictograms. In the case of tires, complete sidewalls may be formed by such an areal member.
The term non-black areal member in the context of the present application is defined as a material of a white and/or colored appearance the composition of which will be explained in detail in this application. In order to avoid confusion as to the term "basic", it is noted herewith that "basic" is used in the chemical sense.
Rubber articles are provided for decorative purposes and/or identification purposes with colored areal member as described above. These areal members, for example, may represent letters, numbers, pictograms, or trademarks. It is, however, also possible to provide sidewalls for tires with such non-black areal members.
The non-black areal members are generally not glued to the rubber articles, but vulcanized onto it. The non-black areal members are thus permanently connected with the rubber base body of the rubber article. However, the anti-oxidant materials contained in the rubber article present a great problem. Conventional anti-oxidants, for example, para-phenylenediamine, are basic and function as radical scavengers. When conventional non-black areal members are applied to rubber articles which contain such basic anti-oxidants, the aforementioned anti-oxidants diffuse slowly into the non-black areal members and react at the exposed top side of the non-black areal member in the presence of light with oxygen contained in the air. Due to the aromatic character of the conventional anti-oxidants dark colored reaction products result. The resulting discoloration of the non-black surface of the non-black areal members have an unpleasant appearance and are rejected by buyers; they are therefore undesirable for the manufacturer.
It has been suggested to design the rubber article onto which the non-black areal members are to be applied without substances that result in discoloration; however, this requires separate manufacturing series for the rubber compounds to be employed and the use of expensive polymers because the use of inexpensive but very effective basic, amino group containing, aromatic anti-oxidants is no longer possible.
The layer of the non-black areal member facing the rubber base body can be comprised of non-polar polymers. These layers made of non-polar polymers impede diffusion of the polar anti-oxidants from the rubber base body into the upper side of the non-black areal member. The disadvantage of this approach for rubber articles with non-black areal members is that a layer of non-polar polymers impedes the diffusion of the polar anti-oxidants to some extent, but cannot completely prevent their diffusion. Accordingly, a discoloration of the light-colored surfaces can only be delayed by means of such a barrier, whereby however this delay is not sufficient to coincide with the service life of the rubber articles.
It is also known to use halides of dicarboxylic acids in order to prevent migration of anti-oxidants from the interior of a rubber mixture to its surface (Derwent 87-194518/28). In the disclosed reference the use of adhesive labels on the tires is also discussed.
However, when using such substances at conventional vulcanization temperatures, volatile hydrogen halides will result. These hydrogen halides have a damaging (toxic) effect on plants and animals including humans, especially by attacking sensitive respiratory organs. Furthermore, the resulting hydrogen halide causes corrosion of metals thereby damages apparatus and devices etc.
It is therefore an object of the present invention to provide environmentally safe rubber articles with non-black areal members, for example, white or colored areal members, whereby the non-black areal members despite the use of basic, amino-group containing, aromatic anti-oxidants in the rubber compound of the rubber article do not result in a discoloration of the areal members.